Sandwich panel

ABSTRACT

An improved sandwich panel is provided by forming the panel filler core with at least one lateral series of symmetrically spaced openings and positioning stress-resisting elements snugly within these opening with the predominant stress-resisting capacity of the elements oriented longitudinally of the panel, and by securing the stress-resisting elements against slippage at the respective inner faces of the panel skin elements.

United States Patent 1191 Hayes Apr. 9, 1974 1 SANDWICH PANEL 3,470,058 9/1969 116111161 52/309 [76] Inventor: obert ay s, do 28 6 3,538,668 11/1970 Anderson 52/615 Bonnieville Dr., Palm Lake FOREIGN PATENTS OR APPLICATIONS s Orlando, 32807 1,492,285 8/1967 France 52/615 1,483,909 6/1967 France 52/615 [22] 1971 1,492,285 8/1967 France 52/615 [21] Appl. No.: 169,277

Primary Examiner-Frank L. Abbott Assistant Examiner-Henry E. Raduazo [52] US. Cl 52/309, 52/615, 55226182262, Attorney Agent, or FirmmRichards Shefte & 1511 1111. c1. E04C 2/20, E04C 2/22 Pinckney [58] Field of Search 52/309, 615, 429, 426,

52/586 [.57] ABSTRACT An improved sandwich panel is provided by forming [56] References C'ted the panel filler core with at least one lateral series of UNITED STATES PATENTS symmetrically spaced openings and positioning stress- 3,383,817 5/1968 Gregori 52/615 resisting ts snug y within these opening with the 3,305,986 2/1967 Mathews 52/309 predominant stress-resisting capacity of the elements 3,471,984 10/1969 Hayes 52/586 oriented longitudinally of the panel, and by securing 2.7251604 1 /1 55 Loetscherm 52/615 the stress-resisting elements against slippage at the re- 31103942 9/1963 52/615 spective inner faces of the panel skin elements. 3,331,174 7/1967 Wesch 52/309 3,462,897 8/1969 Weinrott 52/615 7 Claims, 5 Drawing Figures 1 T T a T T T a T 1 1, t I 1 l 10 i I I 1 l 1 l 1 l 1 I f I ,4 f i r 1"1 I" 1" 1"1 J1 "1 1'1 r 1" i 1 1 1 1 1 1 1 1 I 1 I 1 1 1 1 1 I 1.1 LJ 1.I I- L.' L I. Li L. L1 1 1 1 1 I l6 2 I 1 I 1 I 1 1 i 1 l 1 I i 1 1 1 I I i 1 1 1 1 1 [1 [1 F 1] [i [ll '1 ;'I I": 1'1 1. J 1 I L I ..1 I. L I I..' l 1 1 1 1 3 3 I 1 1' 1 I l I I l 1 1 l I xgle PATENTEUAPR 91974 SANDWICH PANEL CROSS-REFERENCES TO RELATED APPLICATIONS None, although an improvement of the subject matter of my prior US. Pat. No. 3,471,984 is presently disclosed, so that this prior patent is of related interest.

BACKGROUND OF THE INVENTION Sandwich panels of the sort comprising a pair of skin elements having a filler core interposed in sandwich fashion are relatively weak under deflection loading as normally formed, because the tiller core materials commonly used have no appreciable strength in tension or shear. My prior US. Pat. No. 3,471,984, noted above, indicates such normal weakness and discloses an arrangement by which at least one shear block member is additionally secured between the skin elements at an intermediate transverse position to develop unusual strength in the panel structure. When strengthened in this manner, the resulting sandwich panels may be used to good advantage in forming exterior walls, or as roof or floor panels, or for installation in any other situation where the panel must be capable of bearing an imposed load across a structural span within required deflection limits.

However, because the shear block members employed in panel structures in accordance with the foregoing prior patent are arranged in a continuous length extending transversely for at least 75% of the panel width, the use of such shear block members has been found to introduce several problems. First, as wood is the material generally most practical for use in forming such shear blocks, and as millwork tolerances are rather loose, it is difficult to obtain an adequately secure adherence of the shear blocks consistently at the inner faces of the skin elements. Also, the use of continuous shear blocks has made it necessary to install the tiller core in sections, which has not only made formation of the panels more burdensome, but has also impaired the effectiveness with which the filler core could be used for insulation. Additionally, the prior patent arrangement left end grain sections of the shear blocks exposed at the sides of the basic panel structure and thereby readily subject to troublesome pick-up and transfer of moisture along the full block length.

The present invention deals effectively with all of these problems while providing a panel structure of at least equal and in many cases even greater strength.

SUMMARY OF THE INVENTION The sandwich panel of the present invention employs a filler core that is proportioned in length and width so as to be inset at the panel periphery as much as is needed to provide clearance for panel jointing means thereat, and that is otherwise coextensive with the skin elements except for at least one series of symmetrically spaced openings formed therein normal to the skin elements and aligned at an intermediate, transverse position with respect to the panel dimension that will reach across the structural span at which the panel is to be installed.

The filler core openings are provided to receive stress-resisting elements that correspond in depth with the core and that are secured against lateral slippage at the respective inner faces of the skin elements under the loading for which the panel is designed. The stress resisting elements are received snugly in the filler core openings with their length positioned parallel to the span-crossing dimension of the panel, and with the predominant stress-resisting capacity of these elements oriented in the direction of their length. The length of the stress-resisting elements is made at least equal to but not materially exceeding their depth, their width is made sufficient to present adequate surface area for securing at. the inner panel faces but less than the'length, and the aggregate width is made less than 50% of the tiller core, while the number of elements used is such as to provide an aggregate stress-resisting capacity suf ficient to withstand the loading for which the panel is designed within required deflection limits.

The resulting panel structure may be insulated to good advantage because the filler core is minimally in terrupted. In addition, the stress-resisting elements are pocketed in the filler core openings and thereby shielded against moisture pick-up, as well as being individually spaced so that any moisture pick-up at one of them is isolated there. Moreover, the spaced arrange ment of the stress-resisting elements materially increases the unit pressure thereat when the sandwich panel assembly is pressed to set the adhesive bond with the skin elements, so that much more consistent production results as to bond security are obtained, while the production procedure is also facilitated by handling the tiller core as a whole with the stress-resisting elements carried therein. Finally, because the stress resisting elements can be formed in a number of ways to have a predominant stress-resisting capacity in the direction of their length, the spaced arrangement of these elements according to the present invention utilizes them to the best advantage and makes it possible to reduce the extent to which the filler core must be interrupted, as will appear more fully from the detailed description that follows further below.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan of a representative sandwich panel embodying the present invention;

FIG. 2 is an enlarged section detail taken substantially at the line 2-2 in FIG. 1;

FIG. 3 is an end view of one of the stress-resisting elements as seen from the line 3--3 in FIG. 1;

FIG. 4 is a comparable end view of a modified form of stress-resisting element; and

FIG. 5 is a comparable end view of another modified form of stress-resisting element.

DETAILED DESCRIPTION OF THE INVENTION The representative sandwich panel illustrated in FIGS. 1 and 2 of the drawings comprises a pair of skin elements 10 having a filler core 12 interposed in which two lateral series of openings 14 are'formed to receive stress-resisting elements 16 that are secured against slippage at the inner faces of the skin elements 10.

An actualembodiment corresponding to the illustrations of FIGS. 1 and 2 was formed. with 4 feet X 8 feet asbestos-cement (Type U) skin elements 10 of onefourth inch thickness assembled on a 2% inch polystyrene filler core 12 that was proportioned in length and width to be inset 1 inch at the entire panel periphery. The two lateral series of openings 14 were respectively aligned on axes spaced 31 inches from the filler core ends so as to receive and position stress-resisting elements 16 at one-third of the panel length from each end of the skin elements 10. The stress-resisting elements 16 were formed of wood in a depth corresponding to that of the filler core (i.e., 2% inches), and in a length of 2% inches and a width of 1% inches, with the grain of the wood running in the direction of the length. Thefiller core openings 14 were located on 4 inch centers across the panel width and proportioned to receive the stress-resisting elements 16 snugly with their length positioned parallel to the panel length. Eleven elements 16 were symmetrically spaced in each series, so that 2% inches of filler core 12 was left between the elements 16 in each series and 2% inches at each core side.

After securing the skin elements with a suitable adhesive to the filler core 12 and stress-resisting elements 16 in the arrangements noted above, the panel was tested for flexure strength by quarter point loading at a 7 feet 6 inch span in the manner indicated by AST Testing tandar Q ,39,3.- 62,.At.a Q d ,.9i3.Q lbs per sq. ft. (i.e., an applied load of 900 lbs the average deflection recorded was .182 inch, whigh was 19H within the allowable deflection of 0.375 inch specified by the standards for which the panel was designed. Furthermore, it has been found that such panels have excellent deflection recovery characteristics and are readily adaptable with a variety of materials to required strength specifications.

Thus, a further exemplary sandwich panel was constructed with 4 feet X 12 feet skin elements 10 of onefourth inch plywood and a polystyrene filler core 12 of 3% inches depth that was inset 1 inch at the entire panel periphery and formed with four lateral series of spaced openings 14 at successive 28 inch axial locations from the filler core ends to receive wooden stressresisting elements 16 having a depth of 3% inches, a length of 3 /8 inches, and a width of 1% inches. The openings 14 in each series were symmetrically spaced 1% inches apart to position 14 elements 16 in the series spaced nearest each filler core end, and twelve in the series spaced further inwardly so as to stagger the element positions longitudinally of the panel and thereby spread the tensile strain on the panel skins across the panel width. This structure was designed for use as a roof panel and tested well for this purpose.

It should be noted that the 3% inch length of the elements 16 was used in the foregoing construction simply because the means immediately available at the time for cutting the openings 14 in the filler core 12 produced a comparable length to fill, but that no advantage is obtained in extending this length beyond the filler core depth and any extension materially beyond this depth can actually be disadvantageous by introducing an eccentric action of the elements 16 in the panel structure.

It is also notable in particular that when the stressresisting elements 16 are formed of wood the spaced arrangement employed according to the present invention allows them to be oriented with the grain running in the direction of their length to take advantage of the predominant strength of wood parallel to the grain and thereby minimize the extent to which the filler core 12 must be interrupted to accommodate the stressresisting elements 16. Thus, it is possible to maintain the aggregate width of the elements 16 in any one series sufficiently less than 50 percent of the filler core width, so that the spacings between the filler core openings 14 and from each side edge of the filler core can be made at least equal to the individual width of the elements 16. In cases where the tensile strength of the panel skins being used is a critical design factor, the spacing of the openings 14 should be proportioned at about the width of the elements 16 and this width should be reasonably narrow, but considerable latitude is otherwise allowed in arranging the spacing.

In addition, while wood will normally be the best choice of material for use in forming the stress-resisting elements 16 from the standpoint of both simplicity and cost, it is possible to obtain comparable functional advantages with other forms of stress-resisting elements formed of other materials. FIGS. 4 and 5, for example, show alternative forms of stress-resisting elements 16 and 16" of rectangular tube and I section configuration, respectively, suitable for formation of a plastic material or of a metal such as aluminum. In both instances the alternative elements 16 and 16" have predominant stress-resisting capacity in the direction of their length and function comparable to the previously described elements 16.

Sandwich panels embodying the present invention are formed by running a pair of skin elements 10 through adhesive applicator rolls that apply an adhesive coating to the top face of the upper skin element of the pair and the bottom face of the lower one. The

bottom skin element 10 of the first pair is set aside temporarily, while the top is employed to begin a stack of panel structures by superposing a filler core 12 thereon in which stress-resisting elements 16 have been positioned and then covering the superposed filler core 12 and stress-resisting elements 16 with the bottom skin element 10 of a second pair to which adhesive has been applied so that the top skin element of this pair is ready for superposing of a second filler core 12 with elements 16 positioned therein, and so on until a suitable stack for pressing has been built. The bottom skin element 10 of the first pair that was set aside initially is then placed in covering relation at the top of the stack to complete it and the whole is placed in a suitable press to clamp the panel structures of the stack under adhesive setting conditions and at sufficient pressure to bond the structures for practical use.

The present invention has been described in detail above for purposes of illustration only and is not intended to be limited by this description or otherwise to exclude any variation or equivalent arrangement or procedure that would be apparent from, or reasonably suggested by, the foregoing disclosure to the skill of the art.

I claim:

1. An improved prefabricated sandwich panel adapted for installation across a structural span and capable of bearing a givenimposed flexure load at said span within required deflection limits, said sandwich panel comprising a pair of skin elements, a filler core interposed between said skin elements having no appreciable strength in tension or shear and having at least one series of symmetrically spaced openings extending therethrough normal to said skin elements and aligned at an intermediate, transverse position with respect to the panel dimension adapted to reach across said span, said intermediate position being related to the midpoint of said panel dimension, and a flexure stress-resisting element positioned within each filler core opening and secured against lateral slippage under said imposed load at the respective inner faces of said skin elements, said flexure stress-resisting elements having a depth corresponding to that of said filler core, having a length positioned parallel to said span-crossing panel dimension at least equal to but not materially exceeding said depth, having an individual width less than said length but sufficient to present adequate surface area for securing against lateral slippage under said imposed flexure load at said inner panel faces, having an aggregate width less than 50% of the filler core width, and having predominant stress-resisting capacity individually in the direction of said length and aggregate stress-resisting capacity sufficient to withstand said imposed flexure load within said deflection limits.

2. An improved sandwich panel as defined in claim 1 and further characterized in that said flexure stressresisting elements are formed of wood with the grain running in the direction of said length.

3. An improved sandwich panel as defined in claim 1 and further characterized in that said filler core openings are proportioned to receive said flexure stressresisting elements snugly.

4. An improved sandwich panel as defined in claim 1 and further characterized in that the spacing between said filler core openings and from the end openings of said series to the filler core side edges is at least equal to the width of said flexure stress-resisting elements.

5. An improved sandwich panel as defined in claim 1 and further characterized in that said filler core is proportioned in length and width so as to be inset at the entire periphery of said panel to provide clearance for panel jointing means thereat.

6. The method of forming a sandwich panel adapted for installation across a structural span and capable of bearing a given imposed load at said span within required deflection limits, which method comprises applying an adhesive coating to one face of a first skin element, forming a filler core with at least one series of symmetrically spaced openings extending depthwise therethrough and aligned at an intermediate, transverse position with respect to the panel dimension adapted to reach across said span and related to the midpoint of said panel dimension, positioning a flexure stressresisting element corresponding in depth with said filler core in each of said filler core openings, superposing said filler core and flexure stress-resisting elements at the adhesive-coated face of said first skin element, covering said filler core and flexure stress-resisting elements with a second skin element after applying an adhesive coating to the adjacent face of the same, and causing both of said skin elements to adhere to said filler core and flexure stress-resisting elements.

7. The method of forming a sandwich panel as defined in claim 6 and further characterized in that said skin elements are caused to adhere to said filler core and flexure stress-resisting elements by pressing the same under adhesive setting conditions. 

1. An improved prefabricated sandwich panel adapted for installation across a structural span and capable of bearing a given imposed flexure load at said span within required deflection limits, said sandwich panel comprising a pair of skin elements, a filler core interposed between said skin elements having no appreciable strength in tension or shear and having at least one series of symmetrically spaced openings extending therethrough normal to said skin elements and aligned at an intermediate, transverse position with respect to the panel dimension adapted to reach across said span, said intermediate position being related to the midpoint of said panel dimension, and a flexure stress-resisting element positioned within each filler core opening and secured against lateral slippage under said imposed load at the respective inner faces of said skin elements, said flexure stress-resisting elements having a depth corresponding to that of said filler core, having a length positioned parallel to said span-crossing panel dimension at least equal to but not materially exceeding said depth, having an individual width less than said length but sufficient to present adequate surface area for securing against lateral slippage under said imposed flexure load at said inner panel faces, having an aggregate width less than 50% of the filler core width, and having predominant stress-resisting capacity individually in the direction of said length and aggregate stress-resisting capacity sufficient to withstand said imposed flexure load within said deflection limits.
 2. An improved sandwich panel as defined in claim 1 and further characterized in that said flexure stress-resisting elements are formed of wood with the grain running in the direction of saId length.
 3. An improved sandwich panel as defined in claim 1 and further characterized in that said filler core openings are proportioned to receive said flexure stress-resisting elements snugly.
 4. An improved sandwich panel as defined in claim 1 and further characterized in that the spacing between said filler core openings and from the end openings of said series to the filler core side edges is at least equal to the width of said flexure stress-resisting elements.
 5. An improved sandwich panel as defined in claim 1 and further characterized in that said filler core is proportioned in length and width so as to be inset at the entire periphery of said panel to provide clearance for panel jointing means thereat.
 6. The method of forming a sandwich panel adapted for installation across a structural span and capable of bearing a given imposed load at said span within required deflection limits, which method comprises applying an adhesive coating to one face of a first skin element, forming a filler core with at least one series of symmetrically spaced openings extending depthwise therethrough and aligned at an intermediate, transverse position with respect to the panel dimension adapted to reach across said span and related to the midpoint of said panel dimension, positioning a flexure stress-resisting element corresponding in depth with said filler core in each of said filler core openings, superposing said filler core and flexure stress-resisting elements at the adhesive-coated face of said first skin element, covering said filler core and flexure stress-resisting elements with a second skin element after applying an adhesive coating to the adjacent face of the same, and causing both of said skin elements to adhere to said filler core and flexure stress-resisting elements.
 7. The method of forming a sandwich panel as defined in claim 6 and further characterized in that said skin elements are caused to adhere to said filler core and flexure stress-resisting elements by pressing the same under adhesive setting conditions. 